Methods of the initially named type are known.
In the previously known method disclosed in publication U.S. Pat. No. 5,046,098, the front signals L′ and R′ as well as the center signal C and the surround signal S are generated in that the center signal C=a1*L+a2*R and the surround signal S=a3*L−a4*R and the front signals L′=a5*L−a6*C and R′=a7*R−a8*C are formed from the two input signals L and R through summing and difference formation. The coefficients a1 . . . a8 of these weighted summations are derived from level measurements. In order to control this difference formation, two control signals are calculated from the level difference of a left and right channel DLR and from the level difference of a sum and difference signal DCS. These two control signals are changed with time-variant response times in this dynamic. Four individual weighting factors EC, EC, EL and ER, which enable a time-variant output matrix for calculating the front signals L′ and R′ as well as the center signal C and the surround signal S, are then derived from these two time-variant new control signals.
The publication US 2004/0125960 A1, which contains an enhancement of the decoding with time-variant control signals, discloses a further method of the initially named type. The two front signals Lout and Rout are thereby obtained from the two input signals L and R and the subtraction of a weighted sum signal (L+R) and a weighted difference signal (L-R). The center signal C results from the sum (L+R) and the subtraction of the weighted input signals L and R. The surround signal S results from the sum (L-R) and the subtraction of the weighted input signals L and R. The weight coefficients gl, gr, gc and gs are obtained from a level adjustment of the signals L and R or respectively L+R and L−R in a recursive structure.
In publication U.S. Pat. No. 6,697,491 B1, the level difference calculation for L/R and (L+R)/(L−R) also serves to derive control signals for the weighted matrix decoding in the processing of multichannel sound.
In the multichannel sound method described in publication U.S. Pat. No. 5,771,295, the front signals LO and RO, the center signal CO and the surround signals LRO and RRO are derived from stereo signals, i.e., from the input signals L and R. For each of the signals, the respective other signals with a weighting are subtracted from the signals L, R, L+R and L−R. Within the framework of this previously known method for processing a multichannel sound, frequency-dependent weight factors are derived in addition to level ratio calculations. The center signal C thereby only varies in the level, whereas the two surround signals LRO and RRO are derived in two frequency bands and in a phase-inverted manner.
The described methods for processing a multichannel sound in a multichannel sound system were mainly developed for the processing of movie sound signals. It was hereby important to reproduce in a directionally accurate manner dynamically occurring directions of signals, usually in the form of voice and effect signals, spatially over several speakers. The dynamic activation of these multichannel signals supports the directional perception for these types of signals. However, in contrast, the direction information in musical stereo recordings is not dynamic to a high degree, but rather static and only changes slightly for special spatial effects. Acoustic examinations within the framework of the method disclosed in publication US 2004/0125960 A1 show minimal control of the direction information, since dominant directions seldom occur within a stereo mix. This time-variant multichannel control ensures a spatial shift of the signal when a stereo encoding is then performed again.
In contrast, an extraction of direction signal components and their weighting through static or frequency-dependent weighting is considerably more important for a spatial resolution improvement of stereo signals. Thus, the publication WO 2010/015275 A1 represents an important advancement of the method of the initially named type, since the splitting of stereo signals into spatial components takes place here in order to evaluate them with different level regulators. The evaluated spatial signals are then recombined into a stereo signal. Due to the weighting of the spatial signal components, the spatial reproduction of the stereo signal is improved.